Skeletal Muscle Tension Research Articles

Oscillation in resting tension of chick skeletal muscle treated with toxin v from scorpion venom, reduced [calcium] 0 and cadmium

1. 1. An oscillation in resting tension of the chick biventer cervicis muscle is induced by scorpion toxin (CsT-V), reduced [Ca] 0 and by Cd 2+. Other chick muscles, e.g. semispinalis cervicis, anterior and posterior latissimus dorsi, also oscillate with the same treatments. The period of the oscillation in the biventer cervicis muscle is uniform, averaging 5–6 min. 2. 2. The oscillation and the period are very sensitive to changes in temperature, [Ca] 0, [K] 0, ouabain and tetrodotoxin (TTX). The oscillation is resistant to twitch blocking dosages of nicotinic antagonists. 3. 3. The period of the oscillation varies inversely as the temperature (26–37°C), log [K] 0 and [ouabain] and directly as the log [Ca] 0 and [TTX]. 4. 4. These data support the inference that the oscillator is postjunctional and results from fluctuations in the electrochemical gradient of ions across the muscle cell membrane. The role, if any, of the Na +, K + pump in the primary oscillogenic mechanism is not evident from our data.

Continuous monitoring of oxygen tension in human gastrocnemius muscle during exercise

Summary. A technique for continuous monitoring of the intramuscular oxygen tension (i.m. PO2) in human skeletal muscle at rest and during exercise was evaluated. A commercially available oxygen transducer mounted in the tip of a flexible catheter was slightly modified and its characteristics in terms of linearity, response time etc. were investigated in vitro.The oxygen probe was introduced through a cannula into the gastrocnemius muscle often normal subjects and ten patients with peripheral arterial insufficiency. The i.m. PO2 was continuously monitored at rest as well as during fatiguing leg exercise performed on a foot ergometer. The resting i.m. PO2 was 3.83 ± 0.45 kPa in normal subjects and 3.67 ±0.53 kPa in patients with peripheral arterial insufficiency. During exercise a decrease in the i.m. Po2 was found in both patients and normal subjects. At a work load of 8 kg normal subjects exercised for 8.1 ±0.6 min and the i.m. PO2 decreased to 2.45±0.39 kPa. At the same work load (8 kg) the i.m. PO2 decreased to I ‐22±0–4 kPa in the patients although their exercise time was considerably shorter (2.5 ±0.3 min) because of the development of claudication pain. An increase of the work load to 12 kg in the normals reduced the exercise time to 2.2 ± 0.1 min and provoked a more pronounced decrease in the i.m. PO2 (0.99 ±0.01 kPa). The limitations and advantages of the present technique are discussed in relation to other techniques. The results demonstrate that this technique is suitable for measurements of i.m. PO2 in human skeletal muscle tissue during exercise.

The effect of biofeedback-assisted relaxation training on blood pressure and selected biochemical parameters in patients with essential hypertension.

The effect of EMG biofeedback-assisted relaxation on blood pressure and selected biochemical parameters was evaluated in 38 patients with essential hypertension. Training consisted of 8 weeks of biofeedback and home practice of relaxation exercises. Mean blood pressure decreased in the experimental group from 144/90 to 133/84 mm Hg while the control group remained unchanged. Statistically significant decreases in the experimental group also occurred in muscle tension levels, in plasma aldosterone, and in urinary cortisol. Both aldosterone and cortisol are secreted by the adrenal cortex. It was concluded that the technique taught to the experimental group produced a reduction in skeletal muscle tension and a decrease in stress responding mediated by the adrenal cortex.

Exercise hyperemia in the absence of a tissue PO2 decrease.

The relationship between contraction-induced arteriolar vasodilation, estimated blood flow (BF), and tissue oxygen tension (PtO2) in skeletal muscle of young rats was investigated. Arteriolar diameters, BF, and PtO2 were measured during cremaster muscle stimulation at 2, 4, and 8 Hz. At a suffusate PO2 (PsO2) of 5-10 mm Hg, the caliber of second-order arterioles (2A, greater than 30 micrometer diameter) did not significantly increase after 8 Hz stimulation. In contrast, with the same PsO2, third-order arterioles (3A, less than 30 micrometer diameter) significantly dilated to 127 +/- 9 (SE), 135 +/- 12, and 160 +/- 13% of control, respectively at 2, 4, and 8 Hz stimulation. Third-order arteriolar BFs at the end of the stimulation periods were: 119 +/- 18, 176 +/- 14, and 258 +/- 43% of control, respectively. PtO2 remained essentially constant during and following 4 and 8 Hz stimulation if the systemic arterial blood pressure exceeded 80 mm Hg. When PsO2 was increased to 65-70 mm Hg, neither 3A diameters nor PtO2 during 8 Hz stimulation differed from paired comparisons of the response at low PsO2. These data indicate that dilation of small arterioles during increased muscle metabolic activity can occur without a mandatory change in PtO2. This circumstance is unaffected by a substantially increased supply of oxygen to the tissue.

Effects of halothane on functionally skinned rabbit soleus muscle fibers: a correlation between tension transient and 45Ca release.

The mechanism(s) involved in the halothane-induced increase in skeletal muscle contraction was studied using functionally skinned soleus muscle fibers from rabbits: For the tension study, single functionally skinned fibers were individually mounted on two pairs of forceps, with one end attached to a photodiode tension transducer. Ca2+-activated tension development of the contractile proteins, and Ca2+ uptake and release from the sarcoplasmic reticulum (SR) using caffeine-induced tension transients were studied. To measure the amount of calcium, skinned fibers at 0.1 g/ml were used and 0.075 μCi45Ca/ml was spiked in the solution 3 (pCa 6.5 and 1 mM [EGTA]) which promoted rapid loading of Ca2+. Halothane (1–3%) did not change the [Ca2+]-tension relationship; 2 and 3% halothane reduced the maximum Ca2+-activated tension by 6–7%. Halothane (1–3%) added to the solution 3, reduced45Ca uptake by 3, 22 and 23%; however, the subsequent caffeine-induced tension transient and45Ca release were increased by 10–40%. During the release phase only halothane increased both caffeine-induced tension transient and45Ca release by 20–60%. The effects of halothane on the tension transient and on the45Ca release were comparable. There was no dose-response relationship to the effects of halothane on the above parameters. It is concluded that halothane affects the SR by increasing its membrane permeability to Ca2+, resulting in an increase in myoplasmic [Ca2+] and thus in the twitch tension in skeletal muscle.

Calcium-dependent electrical activity and contraction of voltage-clamped frog single muscle fibres.

1. The electrical and mechanical activities of isolated frog muscle fibres have been simultaneously recorded under conditions which allow the development of a calcium permeability (chloride-free solution containing 72 mM-calcium levulinate instead of 115 mM-NaCl). 2. Long-lasting calcium action potentials and large and sustained contraction occur without inhibition of the potassium permeability. 3. The relationship observed between the slow inward calcium current and the amplitude of the contraction, under voltage-clamp conditions, resembles that found between IBa and tension in frog skeletal muscle and between ICa and the contraction in frog heart. A part of the mechanical response which is not abolished by manganese seems to be potential-dependent. 4. Integration of the current traces shows that the threshold of the contraction occurs at [Ca]1 near to 2.10(-6) M and that the contractile proteins are fully activated at [Ca]1 near to 10(-4) M, values which are in good agreement with those proposed by other authors. 5. The minimum calcium influx necessary to induce a detectable contraction is close to 4.8 p-moles/cm2. This value is 10-20 times larger than the calcium influx measured during a normal action potential. 6. On detubulated fibres the calcium permeability fails to develop: this indicates that this current originates from the T-system. The close correspondence between ICa and the contraction, and between the time course of the contraction at the end of the depolarizing steps suggests that the potential of the tubular membrane is better clamped than in normal physiological conditions.

The control of tension and shortening in cardiac and skeletal muscle.

The development of tension and shortening in cardiac and skeletal muscle exhibits phenomena suggestive of control by feedback mechanisms at the molecular level. Two of these, presented here, may have surprising implications for the cross-bridge theory of muscular contraction. It can be argued, from the basis of the cross-bridge theory, that the extended muscle is unstable against further imposed stretch by reason of a corresponding decrease of generated tension. Certain measurements of static tension versus muscle length appear to corroborate this conclusion. On the other hand, there is direct evidence for the dynamic stability of muscle at longer lengths. The cross-bridge theory may be incorrect in this regard, and cross-bridges may contain a negative feedback mechanism; but it may be the case that the contradiction arises out of inappropriately extrapolating the static length-tension data to a dynamic situation. By monitoring the sarcomere length of a contracting muscle, it can be seen that shortening does not proceed smoothly, but in more or less discontinuous jumps. This “stepwise” shortening shows evidence of synchronization across a region of a muscle, and suggests some positive feedback process at work. Some speculations are offered as to possible mechanisms, including load-dependent signalling, diffusion, cooperative effects, and repeated cycles of substrate consumption, concomitant with shortening, alternating with a “catch-up” period of substrate production.

Voluntary heart-rate changes mediated by muscle tension and respiration.

20 undergraduates completed heart-rate mediation treatments (isometric exercise, relaxation, hyperventilation, and hypoventilation) with and without feedback. Heart rate increased during tension, decreased with relaxation, and changed even more with feedback. During hyperventilation the heart rates were lower than during hypoventilation, and this difference was even greater during trials with feedback. This paradoxical finding was attributed to the shallowness of the breathing. Additional data from an experiment on voluntary heart-rate control (n = 31) without feedback and one with biofeedback of heart rate (n = 18) showed that subjects were following heart-rate increase and decrease instructions with altered respiration rates. These observations are interpreted as indicating that biofeedback changes in heart rate are mediated by skeletal muscle tension, respiration, and other mediating mechanisms.

Asthma: The yoga perspective. Part I. The somatopsychic imbalance in asthma: towards a holistic therapy.

While the standard physiological and even certain psychological characteristics of asthmatic patients are well known, the current diagnostic and therapeutic approach to asthma remains inadequate, as it neglects certain interrelated somatopsychic factors vital to an optimal diagnostic-therapeutic programme. These include the role of skeletal muscle tension and posture, the role of the 'voluntary' respiratory musculature, especially the diaphragm, as well as anxiety, emotional suppression and excessive self-consciousness, all of which may be precipitants rather than the outcome of the onset of asthma. On the basis of these neglected factors and others, implications for an optimally effective therapy are discussed. The physical medicine or physiotherapeutic, as well as other recent therapeutic approaches, are reviewed and evaluated. It is concluded that all of these therapies are too "specific," and that a more holistic approach is necessary (which is provided in 'Asthma: The Yoga Perspective,' Part II-"Yoga Therapy in the Treatment of Asthma").

Derivation of reliable electromyograms and their relation to tension in mammalian skeletal muscles during synchronous stimulation

There exists a good correlation between the measured electrical activities and isometric twitch tension in the cat soleus muscle during synchronous stimulation. For an unbiased sampling of electrical activities by averaging a number of electromyograms over the muscle concerned, a relation of the form E = 0.98 T + 535 has been established. It is hoped that this relation will prove valuable in clinical application where EMGs are used. Electrode types for EMG pick-up differ in terms of the signal recorded due to the difference in the spatial and temporal addition of individual motor unit firing and the constructional difference of the electrodes. Fine wire pairs are the best for linearity and ease of application. When surface electrodes are used because of their non-invasive nature, care must be exercised to establish the exact relation between EMG and tension. EMG recordings from different sites within a muscle show considerable variation. A more reliable measure can be obtained by external averaging of multiple pairs of electrodes.

The Dynamics of Contraction in the Guinea Pig Taenia Coli

Tension-length, load-velocity and tension-extension relations were studied in the taenia coli muscle of the guinea pig weighing 0.25--0.5 kg at 36--37 degrees C. The muscle was relaxed by 10(-6) g/ml adrenaline and stimulated by a strong AC field. The tension-length diagram was far wider than that of the skeletal muscle and sufficient tension was generated at longer lengths than 1.8 Lm, where Lm is the optimal length at which the maximum tension, Fm, is generated. The developed force per unit cross-sectional area was almost unchanged between 1.2--2.0 Lm. Average of the maximum forces was 2.2 kg/cm2. Load-velocity curves obtained at various isometric forces at Lm coincided with each other, if the velocity was plotted against the relative force. All curves can be expressed by a single force-load-velocity equation, (P+A)(v+b)=b(F+A), A=(F/Fm)a, where P is the load, F the isometric force, v the velocity, a and b are constants. The maximum velocity per unit muscle length was constant, irrespective of the muscle length. The compliance of the series elastic component, that is, the slope of the tension-extension curve, did not depend on the isometric force but decreased with decreasing muscle length. The internal lengthening of the series elastic component by the full isometric tension was about 3% of the muscle length at Lm.

Verruculotoxin potentiation of twitch tension in skeletal muscle

Verruculotoxin [1-oxo-3-benzyl-octahydro-2H-pyrido(1,2-α)pyrazinel, a mycotoxin, was shown to act directly on both isolated mammalian and amphibian skeletal muscles to potentiate twitch tension. After 10 min exposure to a concentration of 0.4 m m, the twitch tensions of the rat diaphragm and frog sartorius muscles were enhanced to 152 and 150% of controls, respectively. In the isolated frog sartorius muscle, 10 min exposure to verruculotoxin (VTX, 0.4 m m) significantly increased the rate of contraction ( dP dt , 120%), contraction time (CT, 127%), and half-relaxation time ( 1 2 RT , 126%) without significantly changing the twitch duration; in the rat diaphragm preparation, 10 min exposure to VTX (0.4 m m) significantly increased both dP dt (141%) and CT (112%) without altering 1 2 RT and twitch duration. Of the C-15 substituted analogs tested, two analogs, fluoroverruculotoxin and methoxyverruculotoxin, enhanced twitch tension with a potency comparable to that of VTX, while chloroverruculotoxin increased twitch tension to only 120% of control. Hydroxyverruculotoxin and analogs lacking the C-3 benzyl group did not alter the twitch amplitude from control. VTX (0.4 m m, 10 min exposure) reduced twitch tension in the isolated cat papillary muscle to 33% of control. VTX (0.4 m m) was nondepolarizing in endplate and nonendplate regions. Thirty minute exposure to VTX irreversibly increased both the rising phase (sodium influx, 115% of control) and the repolarization phase (115% of control) of the muscle action potential. The results of this study indicate that VTX is a new muscle potentiator with properties similar to caffeine and the other Type A muscle potentiators.

Relation between oxygen uptake and developed tension in dog skeletal muscle.

Isometric developed tension of in situ gastro-cnemius-plantaris and semitendinosus muscles of the dog was increased 30% with twitch contraction frequency over the range of 0.5--2.0 tw/sc. Developed tension was decreased 75% after 30--40 min of 11--14 tw/s contractions, fatigue. Recovery from fatigue was slow. Intravenously injected K+ after fatigue increased developed tension 50%. Infusions of epinephrine, norepinephrine, and ouabain did not change developed tension. When the oxygen uptake of gastrocnemius-plantaris muscle was measured during twitch contractions at 0.5, 1.0, and 2.0 tw/s before and after fatigue and after injection of K+, the oxygen uptake was found to be directly related to the developed tension.

Reversible effect of dantrolene sodium on twitch tension of rat skeletal muscle.

The effect of dantrolene sodium on twitch tension in skeletal muscle of the rat was studied in short- and long-term experiments. The twitch tension is reduced to 50% of the control values within 20 to 30 minutes of drug administration. The recovery phase is considerably slower than the effect observed on the addition of dantrolene sodium, having a half time of 10 hours. Twenty-four hours after the drug injection, the twitch tension in the treated muscles is indistinguishable from that in the controls. It is shown that the reduction in the magnitude of the twitch produced by dantrolene sodium is slowly and completely reversible.

Isometric tension and instantaneous stiffness in amphibian skeletal muscle exposed to solutions of increased tonicity

The instantaneous elasticity and maximum isometric tetanic tension of isolated frog and toad sartorii have been measured in hypertonic Ringer solution. Although the mechanical response of contraction muscle continued to decrease as the tonicity of the bathing solution was increased to 1.26 X R, 1.52 X R, and 2.04 X R, a similar change in the instantaneous stiffness could not be shown. This finding was not expected on the basis of our current model of the cross-bridge mechanism which predicts that the instantaneous stiffness is a measure of the total number of tension-generating cross-bridges formed in a stimulated muscle. The compatability of our findings with an electrostatic theory of the cross-bridge mechanism proposed by Iwazumi (1970) is discussed.

Some effects of organic anions on excitability and excitation–contraction coupling in frog skeletal muscle

When substituted for external chloride, organic anions differed markedly from one another in the extent to which they produced hyperexcitability and in the direction and intensity of their effects on twitch tension in frog skeletal muscle. All of the anions studied reduced the threshold [K]0 for K contractures and most enhanced twitch tension. Among carboxylate anions, increasing the size of the attached apolar hydrocarbon chain led to decreased hyperexcitability and to reduction in the amplitude of twitches and maximum K-contractures, butyrate being the most effective depressant of these responses. Sulfonate anions produced much less conspicuous changes in contractile performance. With γ-hydroxybutyrate, the introduction of a polar group on the hydrocarbon terminus resulted in twitch enhancement and partial restoration of maximum K-contracture tension. The depressant effect of butyrate on K contractures was partially overcome by a fivefold increase in the external concentration of calcium but twitches were unaffected. Perchlorate (12 mM) effectively antagonized the depressant actions of butyrate on twitches as well as K contractures. Most of the effects of these anions were prompt in onset. Impairment of contractile performance by butyrate was not accompanied by appreciable changes in membrane resting or action potentials or in the relation between [K]0 and membrane potential, and took place in spite of reduction in K-contracture threshold. Such effects must result from alteration in excitation–contraction coupling, possibly by interference with the binding of divalent cations to the membrane surface.

Studies on the origin of latency relaxation and resting tension of skeletal muscle: The effect of hypotonic solutions

Latency relaxation (LR) as well as resting tension and twitch tension of frog toe muscles are studied in an isotonic solution (= 1 T) and in solutions made hypotonic by leaving out the appropriate amounts of NaCl and KCl (0.54 T and 0.76 T). In hypotonic solutions there is an increase in peak twitch tension as well as a decrease in the depth of the LR: the resting tension is increased at sarcomere lengths which are greater than 2.8 μm and is decreased at sarcomere lengths which are less than this value. The behaviour of twitch tension is discussed with respect to the influence of the sarcoplasmic ionic strength on the interaction between the contractile filaments. Concerning the decrease in both the LR and the resting tension, it is assumed that these effects are induced osmotically, the tension of the membranes of the longitudinal sarcoplasmic reticulum being the particular parameter which is influenced.

The comparative effects of (Ca2+) and (Mg2+) on on tension generation in the fibers of skinned frog skeletal muscle and mechanically disrupted rat ventricular cardiac muscle.

The effects of intracellular Mg2+ on Ca2+-activated isometric tension generation in rat cardiac muscle fibers and frog skeletal muscle were compared. The membranous sarcolemmal barrier was removed from rat cardiac muscle fibers by mechanical disruption and from frog skeletal muscle by skinning. Tension was recorded in the fibers in bathing solutions of different Ca2+ concentrations and either 5 X 10(-5) M or 1 X 10(-3) M Mg2+ concentration (the same concentrations used in a previous study on single skinned frog skeletal muscle fibers [3]). The amount of Ca2+ required to activate the muscle increased with Mg2+ concentration for both rat ventricular muscle and frog skeletal muscle. These data indicate that intracellular Mg2+ concentration could strongly modulate Ca2+-activated tension in cardiac muscle and that very similar molecular mechanisms are responsible for Ca2+-activated tension in rat ventricular muscle and frog skeletal muscle. The possible sites of action of Mg2+ on Ca2+-activated tension are discussed.

Chemicals as tools in the study of excitable membranes.

Chemicals as tools in the study of excitable membranes.

Studies on the origin of resting tension of skeletal muscle

Glycerol extracted frog skeletal muscle fibres at 2.2 μm sarcomere length (in situ-length) in a solution free of Ca ++ and Mg ++ but containing ATP, show a decrease in both their resting tension and their elastic modulus, if the ionic strength of the bathing solution is increased. This finding is compared with the behaviour of intact skeletal muscle fibres in hypertonic solution. It is concluded that the resting tension of intact skeletal muscle fibres at in situ-length is caused by the longitudinal sarcoplasmic reticulum as well as by interactions between the contractile filaments.